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Heart problems definitely lead to sleep problems, said lead researcher Dr. Lars Laugsand, but his team tried to determine whether the reverse might also be true.
"Insomnia is a frequent and easily recognized, potentially manageable and treatable condition," said Laugsand, a postdoctoral fellow in the department of public health at the Norwegian University of Science and Technology, in Trondheim.
Laugsand added that the researchers found an association between insomnia and heart failure, not that insomnia actually causes heart failure.
"We still do not know whether heart failure is really caused by insomnia, and it is still unclear why insomnia is linked to higher heart failure risk," he said.
Heart failure is a chronic condition in which the heart does not pump blood efficiently enough to meet the body's needs.
There are some indications that a biological cause might explain an insomnia-heart failure connection, Laugsand said. "One possible mechanism could be that insomnia activates stress responses in the body that might negatively affect heart function," he explained.
"If our results are confirmed by others and there is a real causal association, evaluation of insomnia symptoms might have consequences for cardiovascular prevention," Laugsand added.
The report was published March 6 in the online edition of the European Heart Journal.
To measure the effect of insomnia on the risk of heart failure, Laugsand's team collected data on more than 54,000 men and women who took part in a Norwegian study on public health factors between 1995 and 1997. None of the participants had heart failure at the start of the study.
As part of the study, researchers asked about the quality of the participants' sleep and if they had difficulty going to sleep and staying asleep.
After 11 years of follow-up, more than 1,400 participants had developed heart failure, Laugsand's group found. People who had multiple insomnia symptoms had a threefold increased risk of developing heart failure, compared to people who slept well. When depression and anxiety were accounted for, the risk was slightly more than fourfold.
Specifically, having difficulties going to sleep and staying asleep almost every night, and feeling tired in the morning more than once a week, were associated with an increased risk of heart failure, compared to people who never or rarely suffered from these symptoms.
These findings remained even after the researchers took age, sex, marital status, education, shift work, blood pressure, cholesterol, diabetes, weight, physical activity, smoking, alcohol use and previous heart attacks into account.
Dr. Gregg Fonarow, professor of cardiology at the University of California, Los Angeles, said,"Heart failure results in substantial [illness], mortality and health care expenditures."
Insomnia has been associated with an increased risk for cardiovascular events and death, and two earlier studies have suggested that insomnia may also be associated with the risk of heart failure, he noted.
Insomnia can increase the body's inflammatory and stress responses, said Fonarow, who's also a spokesman for the American Heart Association.
"Activation of these systems, as well as other mechanisms, may link insomnia to an increased risk of developing heart failure and other cardiovascular disease," he said. "However, whether preventing or treating insomnia would lower the risk of developing heart failure requires further study."
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